CN114207010B

CN114207010B - Low density polyethylene with enhanced hot tack strength and metal adhesion by addition of ionomers

Info

Publication number: CN114207010B
Application number: CN202080053890.6A
Authority: CN
Inventors: 李中扬; 董一帆; B·A·莫里斯; T·P·卡里亚拉; E-M·库伯什
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2019-07-31
Filing date: 2020-07-30
Publication date: 2024-05-14
Anticipated expiration: 2040-07-30
Also published as: AR119441A1; ES2954634T3; WO2021022010A1; JP2022542177A; MX2022001079A; EP4004106B1; US20220275180A1; CN114207010A; BR112022001345A2; EP4004106A1

Abstract

The present invention provides polymer blends, films, and coated substrates comprising the polymer blends. The polymer blend comprises at least 90 wt% low density polyethylene polymer and 1 wt% to 10 wt% ionomer. The LDPE polymer has a melt index (I ₂) of from 2g/10min to 6g/10min and a molecular weight distribution of from 5 to 11 as determined by conventional gel permeation chromatography. The ionomer comprises an ethylene acid copolymer wherein 15% to 70% of the acid groups, based on the total number of acid groups in the acid copolymer, are neutralized with sodium cations. The ethylene acid copolymer is the polymerization reaction product of at least 50 wt% ethylene, 2 wt% to 40 wt% monocarboxylic acid monomer, and 0wt% to 20wt% alkyl acrylate, based on the total wt% of monomers present in the ethylene acid copolymer.

Description

Low density polyethylene with enhanced hot tack strength and metal adhesion by addition of ionomers

Cross Reference to Related Applications

The present application claims priority from U.S. provisional patent application No. 62/880,837 filed on 7.31 in 2019, the entire disclosure of which is hereby incorporated by reference.

Technical Field

Embodiments of the present disclosure generally relate to polymer blends for extrusion coating having improved hot tack strength and improved adhesion of the polymer blend to metal when compared to LDPE polymers; and to films and coated substrates comprising the polymer blends.

Background

Low Density Polyethylene (LDPE) is widely used in extrusion coating processes for manufacturing food packaging, such as coated paperboard milk cartons and coated films for condiment bags. The LDPE coating provides a hermetic seal to prevent leakage of the product. During the sealing process, the sealing area is heated to melt and bond the sealant. Thermal bonding is the ability of a newly formed seal to remain bonded before cooling back to a solid state. High hot tack strength is required to form a strong seal in the package so that the seal prevents leakage.

Generally, LDPE has poor hot tack strength. This is generally believed to be due to the high level of long chain branching of the LDPE polymer. Long chain branching prevents molecular diffusion at the interface between the two contact surfaces during heat sealing. Such diffusion is required to produce hot tack strength, and lack of diffusion (e.g., highly tortuous paths due to long chain branching) results in low hot tack. The hot tack of LDPE polymers having low melt indices (typically less than 6.0 dg/min) is further reduced. In general, a lower melt index indicates a higher molecular weight, which also slows diffusion at the interface.

Strong peel strength is required to prevent delamination between the coating and the substrate to maintain package integrity. In order for the polyethylene coating to bond to the polar substrate, the polyethylene coating needs to be oxidized. Typically, the polyethylene coating oxidizes in the air gap and at high temperatures for long periods of time. However, this method does not consistently improve peel strength.

Disclosure of Invention

There is a continuing need to produce a polymer or polymer blend that when coated onto a substrate has a peak hot tack strength of greater than 9.5N/inch, wherein the weatherstrip temperature is 120 ℃ to 160 ℃ and the peak load peel strength is greater than 2N/inch.

Embodiments of the present disclosure include polymer blends. The polymer blend comprises at least 90 wt% Low Density Polyethylene (LDPE) polymer and 1 wt% to 10 wt% ionomer. The LDPE polymer has a melt index (I ₂) of 2g/10min to 6g/10min as determined according to ASTM D1238 (190 ℃,2.16kg, procedure B) and a molecular weight distribution (MWD=Mw/Mn, conv.) ionomer of 5 to 11 as conventionally calibrated by Triple Detector Gel Permeation Chromatography (TDGPC) comprising an ethylene acid copolymer wherein 15% to 70% of the carboxylic acid groups are neutralized to carboxylate salts comprising sodium cations. Ethylene acid copolymers are the polymerization reaction product of: at least 50 wt% ethylene based on the total wt% of monomers present in the ethylene acid copolymer; 2 to 30 wt% monocarboxylic acid monomer based on the total weight% of monomers present in the ethylene acid copolymer; and 0 to 25 wt% of an alkyl acrylate based on the total wt% of monomers present in the ethylene acid copolymer.

Embodiments of the present disclosure include coated substrates. The coated substrate includes a substrate; and coatings comprising the polymer blends of the present disclosure.

Drawings

FIG. 1 is a graph of the hot tack strength as a function of the sealing strip temperature for examples 3 and AGILITY EC 7030 ^TM.

Detailed Description

Embodiments of the present disclosure include polymer blends. The polymer blend comprises at least 90 wt% Low Density Polyethylene (LDPE) polymer and 1 wt% to 10 wt% ionomer.

In some embodiments of the polymer blend, the LDPE polymer has a melt index (I ₂) of 2g/10min to 6g/10min as determined according to ASTM D1238 (190 ℃,2.16 kg). In various embodiments, the LDPE polymer has a melt index (I ₂) of 3g/10min to 5g/10min, or 2g/10min to 4.5g/10 min.

In one or more embodiments of the polymer blend, the LDPE polymer has a molecular weight distribution (mwd=mw/Mn) of 5 to 11, 8 to 10, or 8.5 to 11 as determined by conventional gel permeation chromatography.

In some embodiments of the polymer blend, the LDPE polymer is a polymer produced by a tubular reactor. The LDPE polymer may have a density of 0.910g/cc to 0.930g/cc. In some embodiments, the LDPE polymer may have a density of 0.910g/cc to 0.920g/cc, 0.916g/cc to 0.930g/cc, 0.918g/cc to 0.926g/cc, or 0.915g/cc to 0.920g/cc.

In one or more embodiments, the polymer blend includes 1 to 7 wt% or 1 to 5 wt% ionomer. In some embodiments, the polymer blend comprises 3 wt.% to 6 wt.%, 4 wt.% to 6 wt.%, or 5 wt.% to 7 wt.% of the ionomer.

In one or more embodiments of the polymer blend, the ionomer comprises an ethylene acid copolymer, wherein the acid copolymer has 15% to 70% of carboxylic acid groups neutralized to carboxylate salts comprising sodium cations. The percentages are based on the total number of acid groups in the polymer. In some embodiments, the ethylene acid copolymer has 40% to 60%, 30% to 70%, or 40% to 70% of the carboxylic acid groups neutralized to carboxylate salts comprising sodium cations.

Ethylene acid copolymers are the polymerization reaction product of: at least 50 wt% ethylene based on the total wt% of monomers present in the ethylene acid copolymer; 2 to 30 wt% monocarboxylic acid monomer based on the total weight% of monomers present in the ethylene acid copolymer; and 0 to 25 wt% of an alkyl acrylate based on the total wt% of monomers present in the ethylene acid copolymer.

In one or more embodiments, the ethylene acid copolymer is the polymerization reaction product of ethylene monomer, monocarboxylic acid monomer, and optionally alkyl acrylate monomer. The monocarboxylic acid monomer may be present in an amount of 2wt% to 25 wt%, 8wt% to 20 wt%, 5wt% to 23 wt%, 15 wt% to 30 wt%, or 20 wt% to 25 wt%, based on the total weight% of monomers present in the ethylene acid copolymer. The alkyl acrylate may be present in an amount of 0 wt% to 20 wt%, 1 wt% to 10 wt%, or 4 wt% to 15 wt%, based on the total wt% of monomers present in the ethylene acid copolymer.

In some embodiments of the polymer blend, the alkyl acrylate of the acid copolymer may be, for example, but not limited to, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, or a combination thereof. In various embodiments, the alkyl acrylate is a C ₂-C₈ -alkyl acrylate, i.e., an alkyl acrylate having an alkyl group of 1 to 8 carbons.

In various embodiments of the polymer blend, the monocarboxylic acid monomer includes acrylic acid, methacrylic acid, or combinations thereof.

In one or more embodiments of the polymer blend, the ionomer has a melt index (I ₂) as determined according to ASTM D1238 (190 ℃,2.16 kg) of 0.5g/10min to 15g/10 min. In some embodiments, the ionomer has a melt index (I ₂) of 4g/10min to 10g/10min, 0.5g/10min to 10g/10min, or 0.5g/10min to 4g/10 min.

The ethylene acid copolymers can be prepared by standard free radical copolymerization methods, using high pressure, operating in a continuous mode. Monomers are fed into the reaction mixture in a ratio related to the monomer activity and the desired amount of monomer incorporated into the copolymer. In this way, a uniform, nearly random distribution of monomer units along the chain is achieved. Unreacted monomer may be recovered. Additional information regarding the preparation of ethylene acid copolymers can be found in U.S. Pat. No. 3,264,272 and U.S. Pat. No. 4,766,174, each of which is incorporated herein by reference in its entirety.

Additional information about the preparation of ionomers can be found in U.S. Pat. No. 3,264,272A, U.S. Pat. No. 3,322,734A, and U.S. Pat. No. 9,783,352 B2, each of which is incorporated herein by reference in its entirety.

The components may be blended in various ways, for example, dry blending or melt blending the components, as is familiar to the skilled artisan. In one example, the LDPE polymer and ionomer may be dry blended, for example, by adding the components in pellet form in an extruder, where the components are heated and mixed together and then coated on a substrate. Alternatively, the LDPE polymer and ionomer may be melt blended wherein each component is melted and mixed in a compounder or extruder and then pelletized. The pellets were then fed to an extruder to prepare a coated substrate. Other blending methods for mixing the components are contemplated herein.

In some embodiments, the polymer blend does not contain additives. In one or more embodiments, the polymer blend may include additives. The polymer blend may additionally contain minor amounts of additives including plasticizers, stabilizers (including viscosity stabilizers, hydrolytic stabilizers), primary and secondary antioxidants, ultraviolet light absorbers, antistatic agents, dyes, pigments or other colorants, inorganic fillers, flame retardants, lubricants, reinforcing agents (such as glass fibers and glass flakes), synthetic (e.g., aramid) fibers or pulp, foaming or blowing agents, processing aids, slip additives, antiblocking agents (such as silica or talc), mold release agents, tackifying resins, or combinations of two or more thereof. Inorganic fillers such as calcium carbonate and the like may also be incorporated into the blend.

Various embodiments of the present disclosure include coated substrates. The coated substrate includes a substrate and a coating adhered to the substrate. The coating comprises any of the polymer blends disclosed in the present disclosure. In various embodiments, a tie layer is disposed between the polymeric substrate and the coating.

In one or more embodiments of the coated substrate, the substrate comprises a metal substrate, a polymer substrate, or a paper substrate. In some embodiments, the polymeric substrate comprises polyester, polyethylene, polypropylene, polyamide, metallized polyester, metallized polyethylene, metallized polypropylene, or metallized polyamide. In various embodiments, the metal substrate may be aluminum.

In one or more embodiments, the coating of the coated substrate has a peak load peel strength of at least 2/in. In some embodiments, the coated substrate has a peak hot tack strength of at least 9.5N/in as measured by ASTM F-1921 (method B) over a sealing bar temperature range of 120 ℃ to 160 ℃.

Embodiments of the present disclosure include films of polymer blends as previously described. The film is extruded from any of the polymer blends of the present disclosure.

The hot tack strength is the force per unit length in newtons per inch required to pull two films apart in a partially molten state. This test was used to simulate the ability of the package to remain sealed without spilling the contents if the heat seal had not cooled. As the ionomers of the present disclosure are blended into LDPE, the hot tack strength increases, with the temperature range in which hot tack is observed also increasing.

Polymerization

LDPE and acid copolymers used to make ionomers are made by high pressure free radical polymerization. For high pressure, free radical initiated polymerization processes, two basic types of reactors are known. The first type is a stirred autoclave vessel (autoclave reactor) with one or more reaction zones. The second type is a jacketed pipe (tubular reactor) with one or more reaction zones.

The pressure in each autoclave and tubular reactor zone of the process is typically from 100MPa to 400MPa, more typically from 120MPa to 360MPa, and even more typically from 150MPa to 320MPa.

The polymerization temperature in each tubular reactor zone of the process is typically from 100 ℃ to 400 ℃, 130 ℃ to 360 ℃ or 140 ℃ to.330 ℃.

The polymerization temperature in each autoclave reactor zone of the process is typically 150 ℃ to 300 ℃, 165 ℃ to 290 ℃ or 180 ℃ to 280 ℃. Those skilled in the art understand that the polymerization temperature in an autoclave reactor is much lower than that of a tubular reactor, and therefore, more advantageous extractables levels are generally observed in polymers produced in autoclave-based reactor systems.

A tubular reactor having at least three reaction zones may be used to produce the polymer blends of the present disclosure.

To produce the ethylene-based polymers of the present invention (including the LDPE of the present invention), a high pressure, free radical initiated polymerization process is typically used. Typically, a jacketed pipe is used as a reactor, having one or more reaction zones. Suitable, but not limiting, reactor lengths may be from 100 meters to 3000 meters (m) or from 1000 meters to 2000 meters. The beginning of the reaction zone of the reactor is generally defined by side injection of the initiator, ethylene, chain transfer agent (or telomer) of the reaction, and any combination thereof. The high pressure process may be carried out in one or more tubular reactors having one or more reaction zones or in a combination of autoclave and tubular reactors each comprising one or more reaction zones.

Chain transfer agents may be used to control molecular weight. In a preferred embodiment, one or more Chain Transfer Agents (CTAs) are added to the process of the present invention. Typical CTAs that may be used include, but are not limited to, propylene, n-butane, 1-butene, isobutane, propionaldehyde and methyl ethyl ketone. In one embodiment, the amount of CTA used in the process is from 0.03 wt.% to 10 wt.% of the total reaction mixture. The ethylene used to produce the ethylene-based polymer may be purified ethylene, either by removing polar components from the loop recycle stream, or by using a reaction system configuration such that only fresh ethylene is used to make the polymer of the present invention. The requirement to use only purified ethylene to make ethylene-based polymers is not typical. In such cases, ethylene from the recycle loop may be used. In one embodiment, the ethylene-based polymer is LDPE.

Initiator(s)

The process for producing the LDPE polymers of the present disclosure is a free radical polymerization process. The type of radical initiator used in the process is not critical, but one of the initiators preferably used should allow high temperature operation in the range of 300℃to 350 ℃. Examples of suitable free radical initiators include organic peroxides such as peresters, perketals, peroxy ketones, percarbonates and cyclic polyfunctional peroxides. These organic peroxy initiators are added to the reactor in an amount of 0.005 to 0.2 wt.% based on the total weight of polymerizable monomers in the reactor. The peroxide is typically injected in the form of a dilute solution in a suitable solvent, for example in a hydrocarbon solvent.

Other suitable initiators include azodicarbonates, azodicarbonates dinitriles and 1, 2-tetramethylethane derivatives, as well as other components capable of forming free radicals within the desired operating temperature range.

Definition of the definition

Unless stated to the contrary, implied by the context, or conventional in the art, all parts and percentages are by weight and all test methods are current methods truncated to the archiving date of the present disclosure.

The term "blend" or "polymer blend" as used in this disclosure refers to an intimate physical mixture of two or more polymers without chemical reaction between the polymers. The blend may be miscible and have no phase separation at the molecular level, or may be immiscible and exhibit some degree of phase separation at the molecular level. The blend may or may not include one or more domain configurations that can be determined by transmission electron spectroscopy, light scattering, x-ray scattering, and other methods known in the art. The blend may be affected by physically mixing two or more polymers at the macroscopic level or at the microscopic level. Examples of physical mixing at the macroscopic level include melt blending or compounding of resins. Examples of physical mixing at the microscopic level include the simultaneous formation of two or more polymers within the same reactor.

The term "polymer" refers to a polymeric molecule prepared by polymerizing the same or different types of monomers. The generic term polymer thus embraces the terms "homopolymer" and "copolymer". The term "homopolymer" refers to polymers prepared from only one type of monomer; the term "copolymer" refers to a polymer prepared from two or more different monomers.

The term "ethylene-based polymer" or "ethylene polymer" refers to a polymer that comprises a major amount of polymerized ethylene monomer (based on the total weight of the polymer). The ethylene-based polymer and the ethylene polymer may be ethylene homopolymers or may include one or more than one comonomer, provided that the ethylene has the greatest polymer weight fraction among all monomers in the polymer.

The term "monocarboxylic acid monomer" means a molecule having a reactive moiety, such as vinyl or vinylidene, that can be bonded to other monomers to form a polymer and carboxylic acid (-C (O) OH) moieties that are not included in the reactive moiety. For example, (meth) acrylic acid is a monocarboxylic acid monomer in which the vinylidene group is a reactive moiety and a carboxylic acid is present. The term "(meth) acrylic" includes methacrylic acid and/or acrylic acid, and "(meth) acrylate" includes methacrylate, acrylate, or a combination of methacrylate and acrylate.

Test method

Density: samples for density measurement were prepared according to ASTM D1928. The polymer samples were pressed for three minutes at 190℃and 30,000psi, and then pressed for one minute at 21℃and 207 MPa. Measurements were made within one hour of sample compression using ASTM D792, method B.

Melt index: melt index or I ₂ (grams/10 minutes or dg/min) was measured according to ASTM D1238, condition 190 ℃/2.16kg, procedure B.

Triple detector gel permeation chromatography (3D-GPC)

The chromatographic system includes a Polymer Char GPC-IR (Valencia, spain) high temperature GPC chromatograph equipped with an internal IR5 infrared detector (IR 5) coupled to a precision detector (Now Agilent Technologies) 2 angle laser Light Scattering (LS) detector model 2040. For all light scattering measurements, a 15 degree angle was used for measurement purposes. The autosampler oven chamber was set to 160 ℃ and the column chamber was set to 150 ℃. The column that can be used is a 4 Agilent "Mixed a"30cm 20 micron linear Mixed bed column. Chromatographic solvents which may be used include 1,2, 4-trichlorobenzene and contain 200ppm of Butylated Hydroxytoluene (BHT). The solvent source was nitrogen sparged. The injection volume that can be used includes 200 microliters (μl) and the flow rate is 1.0 ml/min.

Calibration of the GPC column set was performed with at least 20 narrow molecular weight distribution polystyrene standards having molecular weights ranging from 580 to 8,400,000, arranged in 6 "cocktail" mixtures with at least ten times spacing, meaning that there is an order of magnitude of about 10 times between the individual molecular weights. These standards were purchased from Agilent Technologies. For molecular weights equal to or greater than 1,000,000, polystyrene standards were prepared at 0.025 grams in 50 milliliters of solvent, and for molecular weights less than 1,000,000, polystyrene standards were prepared at 0.05 grams in 50 milliliters of solvent. Polystyrene standards were dissolved at 80 degrees celsius for 30 minutes with gentle agitation. The polystyrene standard peak molecular weight was converted to polyethylene molecular weight using equation 1 (as described in Williams and Ward, J.Polym.Sci., polym.Let.,6, 621 (1968):

M _Polyethylene＝A×(M_Polystyrene)^B (equation 1)

Where M is the molecular weight, A has a value of 0.4315 and B is equal to 1.0.

A fifth order polynomial is used to fit the calibration points for the corresponding polyethylene equivalent. Minor adjustments were made to A (approximately 0.415 to 0.44) to correct for column resolution and band broadening effects, so that NIST standard NBS 1475 was obtained at 52,000g/mol Mw.

Total plate counts of GPC column set were performed with eicosane (prepared at 0.04g in 50 ml TCB and dissolved for 20 minutes with gentle agitation). Plate counts (equation 2) and symmetry (equation 3) were measured at 200 μl injection according to the following equation:

where RV is the retention volume in milliliters, peak width in milliliters, peak maximum is the maximum height of the peak, and 1/2 height is the 1/2 height of the peak maximum.

Wherein RV is the retention volume in milliliters and peak width is in milliliters, peak maximum is the maximum peak position, one tenth of the height is 1/10 of the height of the peak maximum, and wherein the trailing peak refers to the peak tail at a later retention volume compared to the peak maximum, and wherein the leading peak refers to the peak front at an earlier retention volume compared to the peak maximum. The plate count of the chromatography system should be greater than 24,000 and the symmetry should be between 0.98 and 1.22.

Samples were prepared in a semi-automated manner using the Polymer Char "Instrument control" software, where the target weight of the sample was set at 2mg/mL, and solvent (containing 200ppm BHT) was added to the septum-capped vials previously sparged with nitrogen by a Polymer Char high temperature autosampler. The sample was dissolved at 160℃for 2 hours under "low-speed" shaking.

Based on GPC results, calculations of Mn _(GPC)、Mw_(GPC) and Mz _(GPC) were performed using an internal IR5 detector (measurement channel) of a polymer char GPC-IR chromatograph, according to equations 4-6, using PolymerChar GPCOne ^TM software, an IR chromatogram subtracted at the baseline of each equidistant data collection point (i), and polyethylene equivalent molecular weights obtained from the narrow standard calibration curve of point (i) according to equation 1.

To monitor the variation over time, a flow rate marker (decane) was introduced into each sample via a micropump controlled with the Polymer Char GPC-IR system. This flow rate marker (FM) was used to linearly correct the pump flow rate (nominal)) for each sample by: the RV of the corresponding decanepeak in the sample (RV (FM sample)) was compared to the retention volume of the decanepeak in the narrow standard calibration (RV (FM calibration)). It is assumed that any change in decane marker peak time is related to a linear change in flow rate (effective)) throughout the run. To facilitate the highest accuracy of RV measurements for the flow marker peaks, a least squares fitting procedure was used to fit the peaks of the flow marker concentration chromatograms to a quadratic equation. The first derivative of the quadratic equation is used to solve for the true peak position. After calibrating the system based on the flow marker peaks, the effective flow rate (relative to the narrow standard calibration) is calculated as in equation 7. The processing of the flow marker peaks was done by PolymerChar GPCOne ^TM software. The acceptable flow rate correction is such that the effective flow rate should be within +/-2% of the nominal flow rate.

Flow rate (effective) =flow rate (nominal) ×rv (FM calibration)/RV (FM sample)) (equation 7

The systematic method for determining multi-detector bias was performed in a manner consistent with that published by Balke, mourey et al (Mourey and Balke, chromatographic Polym. Chapter 12, (1992)) (Balke, thitiratsakul, lew, cheung, mourey, chromatographic Polym. Chapter 13, (1992)), whereby triple detector log (MW and IV) results from broad homopolymer polyethylene standards (Mw/Mn > 3) were optimized with narrow standard column calibration results from narrow standard calibration curves using PolymerChar GPCOne ^TM software.

Hot tack strength

The films were subjected to thermal adhesion measurements according to ASTM F-1921 (method B) using a Enepay commercial tester. The samples were conditioned at 23℃and 50% RH (relative humidity) for a minimum of 40 hours according to ASTM D-618 (procedure A) prior to testing. The hot tack test simulates filling a material into a pouch or bag before the seal has an opportunity to cool completely.

Sheets 8.5 inch by 14 inch in size were cut from the coated substrate with the longest dimension being the machine direction. Strips 1 inch wide and 14 inches long were cut from the coated substrate. The sample need only be of sufficient length for clamping. These samples were tested over a range of temperatures and the results reported as the maximum load as a function of the seal bar temperature. Typical temperature steps are 5 ℃ or 10 ℃ and 6 replicates are performed at each temperature. For purposes of this disclosure, testing according to ASTM F-1921 (method B) is accomplished with the following:

sample size: 1.0 inch by 14 inches

Sample width: 25.4mm (1.0 inch)

Sealing pressure: 0.275N/mm ²

Sealing residence time: 0.5s

Delay time: 0.18s

Peeling speed: 200mm/s

Sealing depth = 0.5 inches

Sample thickness = 7.2 mils

Coating thickness = 1.2 mil

Kraft paper=6.0 mil

The data are reported as thermal adhesion curves, where the average thermal adhesion (N) is plotted as a function of temperature. The coated substrate is composed of a polymer extrusion coated onto kraft paper. Kraft paper has a thickness of 6 mils. The coating thickness was 1.2 mils.

The average value (N/in) of the improvement in the hot tack strength was calculated from the following formula (hot tack strength at five seal bar temperatures of 120 ℃, 130 ℃, 140 ℃, 150 ℃ and 160 ℃ were selected for calculation):

Peel strength as measured by peel test

The polymer or polymer blend is extrusion coated onto an aluminum plate (aluminum foil laminated with LDPE and white paper, total thickness of 5.2 mil to 5.5 mil) by an extrusion coating process. The coating was applied to the aluminum side and had a thickness of 1.2 mils. Masking tape is placed over a portion of the aluminum plate prior to extruding and coating the polymer or polymer blend onto the aluminum plate. Because of the weak adhesion between the masking tape and the coating, the masking tape can be peeled from the coating prior to the peel test. Peel test was then used to obtain the peel strength between the coating and the aluminum plate.

Samples were conditioned at 23 ℃ (±2 ℃) and 50% (±10%) Relative Humidity (RH) for a minimum of 40 hours prior to testing the adhesion strength.

The extrusion coated sheet to be tested was cut into 1 inch wide strips in the machine direction with the longer side oriented in the machine direction. The coating was peeled off the aluminum plate (starting from the position where masking tape was present) and then the two jaws of the tensile tester clamped the peeled coating and the end of the aluminum plate. The whole sample was then pulled slowly at a speed of 1in/min to remove the slack. The samples were then tested at a speed of 12in/min and reported for peak and average loads exceeding 3 inches (1 inch to 4 inches).

The peel strength improvement (%) was obtained from the following equation.

Peel strength is the peak load obtained from the peel test, and the reported peel strength is the average of five test samples.

Extrusion coating

Extrusion coating tests were performed using the following standard coating procedure. Briefly, a 3-layer extrusion coating line was used to extrude a single layer coating using only a main 3.5 inch diameter extruder (30:1L/D) powered by a 150HP Eurotherm drive. The extruder barrel consisted of 6 heating zones, zone 1 to zone 6 temperature profile = 179/230/286/316/317/318 ℃ (354/446/546/601/603/605 °f). An internal edge die was used for Cloeren 30 inch hanger EBR III (edge bead reduction) with a 0.5-0.6mm (0.020 ") die gap and 153mm (6 inch) air gap set. The line was equipped with 30 inch chill rolls, nip rolls, backup rolls and a shear slitter.

Extrusion coating was performed at 30gsm (grams per square meter) at 600°f (315 ℃), 90RPM screw speed and 250lbs/hr, 24 inch die width, 20 mil die gap, which converted to a 1.2 mil (30 micron) coating thickness at 440 ft/min.

Examples

The example compositions were prepared and the polymer properties of each composition were measured.

Table 1: examples and comparative compositions and properties of ionomer polymers in blends

* IBA is an abbreviation for isobutyl acrylate.

Table 2: examples and comparative blend composition and properties of LDPE polymers

^TM Trademark of Dow Inc

Examples 1 to 6 and comparative examples C1 to C22 were prepared by first dry blending the LDPE with the ionomer or acid copolymer via a tumble blender, and then adding the blend to the hopper of the extruder to complete the extrusion coating process.

Example 1 is a polymer blend prepared from 95 wt% AGILITY ^TM EC 7000 made by Dow inc as the LDPE component and 5% ionomer 1 made by Dow inc as the sodium neutralized ionomer copolymer.

Example 2 is a polymer blend prepared from 95 wt% LDPE 5005 made by Dow inc as the LDPE component and 5% ionomer 1 made by Dow inc as the sodium neutralized ionomer copolymer.

Example 3 is a polymer blend prepared from 95 wt% AGILITY ^TM EC 7030 as an LDPE component manufactured by Dow inc and 5% ionomer 1 as a sodium neutralized ionomer copolymer manufactured by Dow inc.

Example 4 is a polymer blend prepared from 95 wt% AGILITY ^TM EC 7000 made by Dow inc as the LDPE component and 5% ionomer 2 made by Dow inc as the sodium neutralized ionomer copolymer.

Example 5 is a polymer blend prepared from 95 wt% LDPE 5005 made by Dow inc as the LDPE component and 5% ionomer 2 made by Dow inc as the sodium neutralized ionomer copolymer.

Example 6 is a polymer blend prepared from 95 wt% AGILITY ^TM EC 7030 as an LDPE component manufactured by Dow inc and 5% ionomer 2 as a sodium neutralized ionomer copolymer manufactured by Dow inc.

Comparative example C1 is a polymer blend prepared from 95 wt% LDPE 621I made by Dow inc as the LDPE component and 5% ionomer 1 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C2 is a polymer blend prepared from 95 wt% LDPE 5005 made by Dow inc as the LDPE component and 5% ionomer 3 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C3 is a polymer blend prepared from 95 wt% LDPE 722 made by Dow inc as the LDPE component and 5% ionomer 3 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C4 is a polymer blend prepared from 95 wt% LDPE 4016 made by Dow inc as the LDPE component and 5% ionomer 3 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C5 is a polymer blend prepared from 95 wt% LDPE 4010 made by Dow inc as the LDPE component and 5% ionomer 3 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C6 is a polymer blend prepared from 95 wt% LDPE 621I made by Dow inc as the LDPE component and 5% ionomer 3 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C7 is a polymer blend prepared from 95 wt% LDPE 722 made by Dow inc as the LDPE component and 5% ionomer 2 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C8 is a polymer blend prepared from 95 wt% LDPE 4016 made by Dow inc as the LDPE component and 5% ionomer 2 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C9 is a polymer blend prepared from 95 wt% LDPE 621I made by Dow inc as the LDPE component and 5% ionomer 2 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C10 is a polymer blend prepared from 95 wt% LDPE 722 made by Dow inc as the LDPE component and 5% ionomer 1 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C11 is a polymer blend prepared from 95 wt% LDPE 4016 made by Dow inc as the LDPE component and 5% ionomer 1 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C12 is a polymer blend prepared from 95 wt% LDPE 4010 made by Dow inc as the LDPE component and 5% ionomer 1 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C13 is a polymer blend prepared from 95 wt% AGILITYTM EC 7000 as an LDPE component manufactured by Dow inc and 5% ionomer 3 as a sodium neutralized ionomer copolymer manufactured by Dow inc.

Comparative example C14 is a polymer blend prepared from 95 wt% AGILITYTM EC 7030 made by Dow inc as the LDPE component and 5% ionomer 3 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C15 is a polymer blend prepared from 95 wt% LDPE 4010 made by Dow inc as the LDPE component and 5% ionomer 2 made by Dow inc as the sodium neutralized ionomer copolymer.

Comparative example C16 is a polymer blend made from 95 wt% AGILITYTM EC 7000 made by Dow inc as an LDPE component and 5% acid copolymer a made by Dow inc.

Comparative example C17 is a polymer blend made of 95 wt% LDPE 5005 made by Dow inc as the LDPE component and 5% acid copolymer a made by Dow inc.

Comparative example C18 is a polymer blend made from 95 wt% LDPE 722 made by Dow inc as the LDPE component and 5% acid copolymer a made by Dow inc.

Comparative example C19 is a polymer blend made from 95 wt% LDPE 4016 made by Dow inc as the LDPE component and 5% acid copolymer a made by Dow inc.

Comparative example C20 is a polymer blend made from 95 wt% LDPE 4010 made by Dow inc as the LDPE component and 5% acid copolymer a made by Dow inc.

Comparative example C21 is a polymer blend made from 95 wt% AGILITY ^TM EC 7030 made by Dow inc as an LDPE component and 5% acid copolymer a made by Dow inc.

Comparative example C22 is a polymer blend made from 95 wt% of LDPE 621I made by Dow inc as the LDPE component and 5% acid copolymer a made by Dow inc.

The properties of each polymer blend and comparative polymer are summarized in tables 1-5. The polymers were tested using the method described previously.

Table 3: increased hot tack strength and improved peel strength

* The blend cannot run on an extrusion coating line at line speeds of 440ft/min or greater. (methods of making were previously described)

Calculations for determining the N/in improvement and percent peel strength improvement and hot tack improvement were previously described.

Table 4: examples thermal adhesion Strength of Polymer blends

Fig. 1, a plot of hot tack strength as a function of seal bar temperature, shows that example 3 has a greater hot tack strength than comparative AGILITY ^TM EC 7030. The results in fig. 1 show that the blend of ionomer and LDPE polymer has greater hot tack strength than the LDPE resin.

Table 5: examples peel strength data for polymer blends

Claims

1. A polymer blend, the polymer blend comprising:

At least 90 wt% of a Low Density Polyethylene (LDPE) polymer, wherein the LDPE polymer has a melt index I ₂ of 2g/10min to 6g/10min, as determined according to ASTM D1238 at 190 ℃,2.16kg, using procedure B, and a molecular weight distribution MWD of 5 to 11, as determined by conventional gel permeation chromatography; and

1 To 10 weight percent of an ionomer comprising an ethylene acid copolymer having 15 to 70% of carboxylic acid groups neutralized to carboxylate salts comprising sodium cations based on the total number of acid groups in the polymer, wherein the ethylene acid copolymer is the polymerization reaction product of:

at least 50 wt% ethylene based on the total wt% of monomers present in the ethylene acid copolymer;

2 to 30 wt% monocarboxylic acid monomer based on the total wt% of the monomers present in the ethylene acid copolymer; and

From 0 wt% to 25 wt% of alkyl acrylate based on the total wt% of the monomers present in the ethylene acid copolymer.

2. The polymer blend of claim 1, wherein the LDPE has a density of 0.910g/cc to 0.930g/cc and a molecular weight distribution of 8.5 to 11 as determined by conventional gel permeation chromatography, wherein density is measured using ASTM D792, method B.

3. The polymer blend of claim 1, wherein the LDPE has a melt index I ₂ of from 2g/10min to 4.5g/10 min.

4. The polymer blend of claim 1, wherein the ionomer has a melt index I ₂ of 0.5g/10min to 15g/10 min.

5. The polymer blend of claim 1, wherein the ionomer has a melt index I ₂ of 0.5g/10min to 4g/10 min.

6. The polymer blend of claim 1, wherein the polymer blend comprises from 1wt% to 5wt% of the ionomer.

7. The polymer blend of claim 1, wherein the ionomer has 40% to 60% acid groups neutralized with sodium cations based on the total number of acid groups.

8. The polymer blend of claim 1, wherein the ethylene acid copolymer comprises at least 70 wt% ethylene and 8 wt% to 25 wt% monocarboxylic acid monomer.

9. The polymer blend of claim 1, wherein the ethylene acid copolymer comprises at least 70 wt% ethylene and 8 wt% to 20 wt% monocarboxylic acid monomer.

10. The polymer blend of claim 1, wherein the alkyl acrylate comprises methyl acrylate, ethyl acrylate, n-butyl acrylate, or isobutyl acrylate, or a combination thereof, and the monocarboxylic acid monomer comprises one or more of acrylic acid, methacrylic acid, or a combination thereof.

11. A coated substrate, the coated substrate comprising:

A substrate; and

A coating comprising the polymer blend according to any one of claims 1 to 10 adhered to the substrate.

12. The coated substrate of claim 11, wherein the substrate comprises a metal substrate, a paper substrate, or a polymer substrate.

13. The coated substrate of claim 12 wherein the polymeric substrate comprises a polyester or a metallized polyester.

14. The coated substrate of claim 12 wherein the polymeric substrate is metallized.

15. The coated substrate of claim 12, wherein the polymeric substrate is polypropylene, polyethylene, metallized polypropylene, or metallized polyethylene.

16. The coated substrate of claim 11, wherein the coated substrate has a peak hot tack strength of at least 9.5N/in as measured by ASTM F-1921, method B, in a seal bar temperature range of 120 ℃ to 160 ℃.

17. The coated substrate of claim 11 wherein the coating has a peak load peel strength of at least 2N/in as measured by a peel test.

18. A film comprising the polymer blend of claim 1.